1. Field of the Invention
The present invention relates to a sealing structure, and particularly to a connecting structure between a fluid supply member and a fluid receiving member which receives a fluid from the fluid supply member. For instance, the invention relates to a structure of connecting a head unit with an ink supply member via an elastic member to receive an ink from the ink supply member, in an inkjet printer which ejects droplets of the ink from a plurality of nozzles onto a recording medium to record information or an image.
2. Description of Related Art
JP-A-2003-145791 (see FIGS. 5 and 10) discloses a sealing structure in an inkjet printer including an ink source, an elastic tube, an ink tank as a fluid supply member and a head unit, and a carriage on which the ink tank and the head unit are mounted. An ink is supplied from the ink source to the ink tank through the tube, and the ink tank and the head unit are connected with each other to allow ink communication therebetween. An O-ring is disposed at the connection between the ink tank and the head unit.
JP-A-2003-237072 discloses a liquid-droplet ejecting apparatus including a tank storing a recording liquid, a head chip for ejecting droplets of the recording liquid therefrom, a frame body holding the tank and the head chip, and a sealing member disposed at connection between the head chip and the frame body.
The sealing member disclosed in the latter publication has a plate-like body in which a through-hole is formed to supply therethrough the recording liquid from the tank to the head chip. On each of two opposite surfaces of the plate-like body, a double rib, namely, a combination of an inner annular rib and an outer annular rib, is disposed along a circumference of the plate-like body and on the radially outer side of the through-hole. The double ribs on the opposite surfaces of the plate-like body are symmetrical to each other in position and in shape with respect to the plate-like body. A positioning protrusion is formed on one of the opposite surfaces of the sealing member, on the radially inner side of the inner annular rib and on the radially outer side of the through-hole, so as to facilitate positioning of the sealing member, that is, the positioning protrusion is fitted in a blind hole formed in one of two members which hold the elastic member therebetween. According to the sealing member, at the connection between the head chip and the frame body, a high liquid-tightness or sealability is obtained without close or tight engagement of the head chip with the frame body, such as fitting.
In addition, the present applicant has devised a sealing structure for liquid-tightly connecting an ink tank storing four inks, with a cavity unit of a head unit held by a head holder, via an elastic sealing member and a reinforcing frame interposed between the elastic sealing member and the head unit, for supplying the inks in the ink tank to the cavity unit. The elastic sealing member has a plate-like body in which four through-holes are arranged in a row. Four discrete first protruding portions are formed on one of two opposite surfaces of the plate-like body to encircle open ends of the respective through-holes. That is, each of the first protruding portions is annular in plan view. A single second protruding portion, which is also annular in plan view, is formed on the other surface of the plate-like body, to encircle the other open ends of all the through-holes. Four ink outlet ports open in an under surface of the ink tank and four ink inlet ports open in an upper surface of the cavity unit are connected to each other via the through-holes in the elastic member and four through-holes formed in the reinforcing frame. On the under surface of the ink tank, there are formed a double rib, namely, a combination of four inner annular ribs encircling open ends of the respective ink outlet ports, and a common outer annular rib disposed on the outer side of all the inner ribs to define a groove between the inner ribs and the outer rib. With the second protruding portion of the elastic member fitted in the groove, the ink tank is screwed to the reinforcing frame, thereby compressing the elastic member to hold the first protruding portions in close contact with the reinforcing frame and to hold the second protruding portion closely fitted between the inner ribs and the outer rib of the ink tank, that is, closely fitted in the groove.
This sealing structure by the present applicant has several drawbacks.
First, when the first protruding portions of the elastic member are brought into close contact with the reinforcing frame, it is impossible to visually check whether the first protruding portions are perfectly contacted with the reinforcing frame, due to presence of the head holder. Where the first protruding portions are not properly positioned with respect to the reinforcing frame, ink leakage will occur.
Secondly, the first protruding portions of the elastic member may be displaced or deformed to incline due to a compressing force imparted on the elastic member upon screwing of the ink tank to the reinforcing frame. In particular, outermost two of the first protruding portions arranged in a row tend to deform. When the elastic member is compressed, the plate-like body of the elastic member, which is in contact with the ink tank, receives a force from the ink tank. At each of two opposite outermost portions of the plate-like body in a direction of arrangement of the first protruding portions, i.e., a direction of a row of the first protruding portions, the elastic member protrudes, in the form of a first protruding portion, toward the reinforcing frame, only at a side of or adjacent to the through-hole. In other words, extreme end portions of the plate-like body in the direction of the row of the first protruding portions are not supported by a first protruding portion from the under side. Hence, the force from the ink tank tends to incline, inward or to the side of the through-hole, a linear part of each outermost first protruding portion, which part is on the outer side in the direction of the row of the first protruding portions. This leads to deterioration in the liquid-tightness or sealability between the first protruding portions and the reinforcing frame.
Thirdly, since inner circumferential surfaces of the ink outlet ports and ink inlet ports, and those of the through-holes of the elastic member are disposed to cooperate to constitute four substantially continuous circumferential surfaces each defining an ink passage therein, it may occur that some one of the first protruding portions deforms or inclines to be located in the through-holes of the elastic member, or falls into the through-holes of the reinforcing frame or the ink inlet ports formed in the cavity unit when the first protruding portions are positioned with great error with respect to the reinforcing frame, or when the compressing force is too great. Such deformation or inclination of the first protruding portion leads to deterioration in the sealability that may result in ink leakage from the outermost portions of the plate-like body in the direction of the row of the through-holes.
When the sealability offered by the sealing structure is deteriorated due to any of the above-described reasons, an ambient air may be introduced into the ink passages, or mixing of colors of the inks may occur due to leakage of the inks. Hence, in manufacture of an inkjet printer including the sealing structure, the sealing structure is inspected for defects in regard to the connection of the elastic member, that is, an inspection for ink leakage is implemented, to get rid of a defective piece. Due to inclusion of this inspection step, the production cost of the inkjet printer increases. Further, when any piece is determined to be defective in the inspection, not only the elastic sealing member but an entirety of the head holder, in which the elastic member is mounted together with other members such as the ink tank and the head unit, is wastefully discarded.
Fourthly, since the elastic member functions to seal the connection between the ink outlet ports and the through-holes of the reinforcing frame, by the second protruding portion thereof being closely fitted in the groove while end portions of the first protruding portions being contacted with the reinforcing frame to receive a compression force therefrom, the elastic member should have a sufficient dimension in an axial direction of the through-holes of the elastic member, to accommodate a variation in an amount by which the end portions of the first protruding portions are compressed, which variation results from a variation in the compressing force. Displacement or the deformation or inclination of the first protruding portions as described above may be eliminated by reducing the dimension of the elastic member in this direction (hereinafter, a dimension of any member or part in the axial direction of the through-holes of the elastic member, which is parallel to an axial direction of the ink inlet ports and of the ink outlet ports, may be simply referred to as a “height” of that member or part). However, when the height of the elastic member is reduced, the load that the elastic member receives inevitably increases because the first protruding portions should be compressed by a sufficient degree to ensure a sufficient sealability. In this case, a reacting force from the elastic member to the increased load acts on the ink tank and the head unit that are in direct and indirect contact with the elastic member, respectively. This may cause undesirable deformation of the ink tank and the head unit.
Meanwhile, to meet demands for higher print rate, recent inkjet printers are enhanced in the print rate and increased in the number and density of nozzles arranged in the cavity unit, with increase in an amount of ink ejected per unit time. On the other hand, there is a demand for reduction in the size of the inkjet printers, too, and thus components of the recent inkjet printers are reduced in the overall size and thickness. In view of these trends, it is not desirable to increase the size of components that relate to ink supply, such as ink tank and ink outlet ports, even though increase in the size of these components can contribute to enable increase in the amount of ink ejected per unit time. In the above-described sealing structure using the O-ring, for instance, a diameter of the O-ring may be increased to enable increase in the ink consumption rate, but the increase in the diameter of the O-ring leads to increase in the size of the head unit. In addition, when the O-ring is assembled, or fixed to a relevant engaging portion, a portion of the O-ring, a height of which is half a total height or thickness of the O-ring, should be engaged with the engaging portion, and thus the O-ring is compressible only by an amount or a height corresponding to the rest half of the O-ring at the maximum when receiving a compressing force from two members holding the O-ring therebetween. Thus, the maximum amount by which the O-ring is compressible is relatively small which means that the O-ring can not contact sufficiently tightly with the members holding the O-ring therebetween, or can not provide a desired sealability.